Why does my RCD keep tripping?

You can do most of this yourself in about ten minutes, and it will save you money whoever you call.

If the RCD resets and immediately trips again with nothing plugged in and every breaker off, stop there and phone an electrician — that points at a fault in the fixed wiring rather than in something you own.

A single faulty appliance is by far the most common cause. Anything with a heating element and a hard life is a candidate: kettles, tumble dryers, washing machines, immersion heaters, old fridges, hair straighteners. Their element insulation degrades and starts leaking current to earth. Very often it only leaks once the element is hot, which is why the trip happens twenty minutes into a wash cycle rather than the moment you switch it on.

Water is the next one. Rain driving into an outside socket, a leaking roof over a light fitting, a shower pull-cord in a steamy bathroom, water finding a buried cable after someone put a nail through it. Outdoor circuits that only trip when it rains are telling you something quite specific.

Then there's cumulative earth leakage. Every appliance leaks a tiny amount of current to earth quite legitimately — TVs, computers, LED drivers, induction hobs, boilers, EV chargers. Individually they're nothing. But if a single 30 mA RCD is covering half the house, add enough of them together and you can sit at 20-something milliamps all day long. Nothing is faulty; the RCD is simply close to its limit, so the smallest extra nudge tips it over. That's the classic 'it trips for no reason, usually in the evening when everything's on' fault, and it's a design problem, not a broken appliance.

Finally, borrowed or crossed neutrals. Older lighting circuits — particularly ones that have been extended by a previous owner, or where a two-way landing switch has been rewired badly — sometimes end up with the neutral of one circuit connected to another. Add an RCD to that and it trips the instant both circuits are used together. It is a common one in houses that have been part-rewired over the years.

An older board typically has one or two 30 mA RCDs, each protecting a whole bank of circuits. Nuisance-trip a board like that and you lose the lights, the sockets, the freezer and the alarm all at once, and you're left guessing which of thirty things caused it.

A board built with RCBOs gives each circuit its own combined overload and earth-leakage protection. A fault on the garden lights takes out the garden lights, and nothing else — the fridge stays cold, the router stays on, and you know instantly where to look. That's the practical argument for the change, and it matters more than the compliance one to most people living in the house.

It also removes the cumulative-leakage problem, because each circuit's leakage is now measured on its own instead of being added into a pile.

Treat it as urgent, not annoying, if any of these are true: the RCD won't reset at all with everything switched off; there's a smell of burning or hot plastic near the board or a socket; there's scorching or melting anywhere; the trips started after water got in; or the board is warm to the touch.

In those cases leave the power off to the affected part of the house and call someone. An RCD that refuses to reset is usually not a faulty RCD — it is an RCD that has found something and is holding its ground.

If you're in Doncaster or nearby and you'd rather someone just came and traced it properly with a test instrument instead of you playing switch roulette for a fortnight, call Lewis on 07467 381272.